Method of humidifying air



Sept. 16, 1941. w. w. CUMMINGS, JR

METHOD OF HUMIDIFYING AIR Filed Sept. 24, 1940 Int/anion fli ' Patented Sept. 16, 1941 UNITED STATES PATENT OFFICE F mm; Am William warren'cunilznings, Jr., Marshfleld,

Application September 24. 1940. Serial No. 358,116

3 Claims. (01. 183-23) outlets for distribution of moisture.

The present application is a continuation in part of my co-pending application Serial No. 313,387, filed January 11, 1940.

Humidifiers heretofore in use, so far as I am aware, all operate upon the principle of carrying the moisture in suspension or entrained in the air and distributing it by having large numbers of sprays throughout the area to be humidified, or by forcibly circulating the processed air throughout the area by large ducts. Thus steam l5 principle of ejecting fine particles of moisture into the air. My system, on the other hand, seeks to eliminate all the fine particles of moisture carried in suspension in the air, and to rely solely upon vapor pressure differential for distribution of the moisture. By so doing, my

method overcomes and eliminates the many disadvantages of these previous systems, makes possible great economies in air humidificatiom both in cost of installation and operation, and at the same time provides greater efllciency of operation and control.

The distinction between my method 'and previous methods or humidification is best brought out, because of their superficial similarities, by aocomparison of my method with the .central washer system in common use. The central washer system circulates the room air through the unit by means or large ianaand water is. sprayed into the air while. beingcirculated through the unit, and the moisture is'then car- 40 ried in suspension and distributed about the area to be humidified by-means of large ducts, which extend into every portion of the area. The mols- 'ture particles, being heavier than air, would otherwise drop to the floor and not circulate it not carried by a rapidly moving current of air. Because of heat losses due to moisture evaporation, the air is occasionallyheated up to room temperature before being elected into the room,

to maintain the room temperature. In some in-'. stancesthe water itself maybe heated for the same purpose. But in no case is the air or water heated to create a high vapor pressure or to distribute the moisture by vapor pressure difi'ersuch a system is wholly insuflicient and is not relied on to distribute the moisture. A low vapor pressure diflerential will not suiiice' because it will not have sufiicient force of distribution 5 and will lose' its temperature before proper distributional moisture can occur, and so cause precipitation. The moisture is distributed by means of fans forcing the air through large ducts which extend to every portion oi the area to be humidified and for proper humidification large quantities or air must be continuously circulated. To take a typical installation, where a room area 01' 50,000 cubic feet is to be maintained at 70 F., and 50 percent relative humidity with 0 Ft, temperature outside (which carries practically no moisture), the central washer system at the minimum is required to circulate 40 pounds or 280,000 grains of water per hour, or 4,666.6 grains per minute. As 110 grains of water per pound of air is the maximum carrying capacity or saturation point of air at room'temperature, 70 F., and the room. air entering the unit is already at approximately 50 percent humidity, containing grains of water per pound of air, the capacity of the system to deliver additional and surplus moisture is the difference, or only 55 grains perpound of air. To deliver such 55 grains, 934 pounds chair or 13,076 cubic feet of air per minute are required to be delivered (obtained by dividing 4666.6"grains per minute by 55, and multiplying by 14 cubic feet, the volume of air per pound at F.) As this amount of air entering the unit at 70f FL, loses 20 temperature in passing through," which at least halves the moisture-carrying capacity of the airfland if heat is not applied to bring the processed air upv to '10 in, 26,000 cubic feet of air per minute (at 50" F.) are required to carry this amount of moisture. If heat is applied to the processed. air to oflset the heat loss due to vaporization, the 13,076 cubic i'eet of air per minute will sufilce. Without the heat, therefore, the air must be changed once every 2 minutes or 30 times per hour, and'it heated, once every 4 minutes or 15 times per hour. To distribute such a vast 'quantityof air large duct work and fans are required. In winter, the complete changing of air as much as 15 times per hour isvery undesirable, because, it causes drafts and is injurious to health. To avoid this, system of much largercapacity are intalled, to permit the air to be changed less frequently. The cost of installation of a unit designed to maintain these conditions, with the -ential. 'Whatever vapor pressuremay exist in 5 large tans. motors, pumps and duct work recentral washer type.

quired, is at least $10,000. The problem of condensation is an additional difficulty, with long and extensive ducts, for if a draft condition occurs anywhere, the moisture will condense and must be drained off. At the same time, with every drop in temperature of 1'7 'F., the moisture-carrying capacity of the air is out in half. Draft conditions, therefore, seriously impair the efiiciencyof the system and require insulation of the ducts to prevent cooling and condensation.

My system, briefly, involves creating a high vapor pressure differential by heating a quantity of water and air, and releasing the vapor at high pressure into the room to be controlled, and relying upon the high vapor pressure differential to carry the water vapor into the far comers of the room by quickly equalizing with the vapor pressure therein. The vapor pressure created by the unit must be high enough to carry the vapor throughout the area to be controlled by itself, without independent carrying means, and to do so before its temperature loss can cause precipitation, and to carry sufllcient heat in latent form so as not to materially affect the sensible heat of the controlled area. I seek to avoid entirely the carrying of particles of moisture in suspension, because of the condensation problem they create, their cooling effect on the room temperature and the large volumes of air they require to hold them in suspension. Thus, large fans and duct work for distributing the moisture by circulating large quantities of air are unnecessary and can be eliminatedr A unit embodying my method and humidifying the same area and maintaining the same conditions as above need circulate only 250 cubic feet of air or vapor per minute, and such a unit can be installed for $1000, and can be operated for considerably less than a corresponding With my high vapor pressure the condensation problem is entirely eliminated because, before a temperature drop occurs, sumcient to cause condensation, the vapor has already equalized and dispersed. The degree of vapor pressure required in any instance is a mere matter of computing the requirements of the particular job, and is determined by the capacity of the unit to deliver processed air, the amount of moisture required to be replaced in any given amount of time, the vapor pressure required to carry it throughout the area before temperature loss occurs which can cause precipitation, and the latent heat of the vapor so as not to upset the temperature of the controlled area. The temperature to which the water and air is heated in any particular instance likewise depends upon the vapor pressure required. The temperature of the water will run between 100 F., and its boiling point, and the temperature of the air will in general correspond, but can be higher. Such computations can be made by'any competent humidiflcation engineer, after he understands my method of hmnidiflcation, and a practical example is given below in the specification.

Before explaining in detail the present invention it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustra/ted in the accompanying drawing, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation, and it is not intended to limit the invention claimed herein beyond the requirements of the prior art.

In the drawing:

vFig. 1 is a longitudinal section through a humidifier capable of performing in accordance with the present, novel method.

Fig. 2 is a longitudinal section through a modifled humidifier.

Referring to the drawing and-particularly to Fig. 1 thereof, the reference numeral l0 designates a suitably constructed container which is closed except for an air inlet l2 and an air outlet l4. The container is preferably placed in the enclosed space whose air is to be humidified. Suitably mounted in the container at the inlet l2 thereof is a conventional shell and tube-type heat-exchanger 18 through which air must pass and be heated in order to enter the container in the manner indicated by the arrows I. Also provided in the container III by transverse partitions 20, 22 is a reservoir 24 which contains water. Water from any suitable source is admitted to the reservoir 24 through a valve 26, having a conventional air-filled float 28 for controlling the valve so that the water level remains substantially constant. A suitable pump 30, driven by an electric motor 82, has its intake side in permanent communication with the water supply in the reservoir through a conduit 34, while its discharge side communicates through a conduit 38 with the intake end of any suitable heater coil 38 in a shell 40,whose bottom end is open to admit the heat from a gas burner 42 and whose top end communicates with a flue (not shown) for the escape of the products of combustion. The gas burner 42 has a conventional automatic pilot which ignites the burner when gas from any suitable source is admitted through a conduit 44. It is to be understood, or course, that other sources of heat may be used instead of the gas flame, such as steam, oil, electricity and the like. The discharge end of the heater coil 38 communicates through a conduit 50 with the water intake end of the heat exchanger l6 through which water flows counter to and separated from the flowing air therein and in heat-exchange relation with the latter. The water discharge and of the heat exchanger 16 is connected through a conduit 52 with a spray nozzle 54 which is adapted to spray hot water through the flowing heated air in the container and into the reservoir 24. Suitable transverse bailles 56 and 58 in the container cause the heated air to flow counter to the water spray from the nozzle 54 as indicated by the arrows 59. A horizontal partition 60 in the container together with the previously mentioned partition 20 therein form not only a separate chamber 62, in which the motor driven pump 30 and the water heater 38, 40 and 42 are housed, but also an air duct 64 from the inlet I2 to the reservoir 24. Provided on the earlier mentioned baflie 58 and partition 22 and on an intermediate partition 86 are eliminator plates 68 past which the heated and sprayed air flows in the manner indicated by the arrows .10. These eliminator plates remove any moisture in suspension from the air stream. It is to be understood, however, that the eliminator plates may be dispensed with and moisture in, suspension may be largely prevented by adjusting the velocity of the water spray. Suitably mounted in the container I0 as on the pedestal 12, for instance, is a motor-driven fan 14 whose discharge end communicates with the outlet I4. The fan 14, when operating, draws air into the container through the inlet i2 and causes it to flow therein in the manner indicated by the arrows II, it and II before being expelled through the outlet I4.

I Any suitable automatic means (not shown) such as a humidostat may beused to 'startand control the operation of the motor-driven pump 30, burner 42 and motor-driven fan I4 in accordance with the varying demands for humidity. When the pump ll, burner 42 and fan 14 operate,

water from the reservoir 24 is forced through the heater coil 38 and then through the heat exchanger l6 from where it passes to the spray nozzle 54 and thence back to the reservoir. While different vapor pressures in diflerent air masses will almost instantaneously equalize to a common vapor pressure when said air masses come in contact with each other. Actual tests have shown that vapor transfer takes place from a higher to a lower pressure even where the vapor has to travel counter to an air stream such as one having a velocity of 3000'feet per minute, for instance. Vapor will, therefore, flow from a higher to a lower pressure independently of any air motion. Thus,'where the vapor pressure high in one part of a room and lower in the rest of the room, the high vapor pressure will quickly disperse and distribute its moisture evenly, inde-v pendently of any air motion, to the rest of the room until the vapor pressure throughout the room isuniform. I use this principle to great advantage in the present humidifying method to distribute the moisture evenly throughout the controlled area, independent of other carrying means, and for this purpose I obtain a very high vapor pressure in the air treated in the container. In order to accomplish this, the air in the container must have the hightemperature at which such a high vapor pressure is possible. As the vaporization of the considerable moisture added will entail considerable heat losses. considerable heat has to be furnished in excess of that required to bring the air, which is to carry the added moisture, to said high temperature. The spray water asv well as the flowing air in the container are accordingly heated to the requisite high temperatures by the water heater II and by the heatexchange between the heated water and the indrawn air in the exchanger it.

As a practical example of the applied method,

if a heated room. is sought to be maintained at a temperature of 80 F., and 40 percent relative humidity (.44 inch of mercury vapor pressure) this can be done by heating the spray water in the heater coil 3! to approximately 180 F., while the indrawn air because of heat losses is being heated in the exchanger i6 and by water spray from the nozzle 54 to an approximate tem-- perature of 150 F. Due to the heat losses on account of the evaporation of the moisture, the temperature of the air at the outlet of the container drops to approximately 104 F., and its relative humidity is around 80 percent, corresponding to a water vapor pressure of 1.4inches of mercury. Hence the vapor pressure differential at the outlet of the container and in the rest of the room is 1.4 minus .44 or .96 inch of mercury column, with the result that the vapor flows immediately from the higher pressure to the lower pressure. For other conditions, as for humidifying the otherwise conditioned air of a large hall or workshop, for instance, the vapor pressure of the air treatedln a small size humidifier may be raised to 3 or 4 inches of mercury column, by increasing the temperature of-the air, or the water or both, and the ensuing flow of vapor may suiflce to humidify the ,air in said hall or workshop satisfactorily. The'precise temperature of the water (below its boiling point) and of the air,

1 in any instance, is dependent upon the vapor pressure required in that instance, which in turn is dependent upon the volume of the area to be Relative humidity, percent 10 75 assets.

assess assess assess My method constitutes a radical departure from the accepted mode of humidifying air by the hitherto known conditioners which are more or less general purpou units attempting humidiflcation besides performing other air-conditioning functions such as heating, cleaning the air, etc. These known conditioners rely for the distribution of the added moisture, on large volumes of air currents which carry most of the moisture in suspension and not in a gaseous vapor state. Large volumes of air currents moreover change the temperature of the air in the room to be treated so that the known conditioners are not at all usable where otherwise conditioned air. is

to be kept at a certain temperature and humidity, as in a variety of industrial plants, for instance.

As in the present method air motion takes no part in the distribution of the vapor under high pres-' sure, the transmission of the sensible heat of the treated air in the unit to the airin the room may be curbed tosuch an -extent that the temperature of the room air is not noticeably changed. Thus, a very small volume of air in the unit capable of carrying a large quantity of,moisture, as vapor under high pressure, is suflicient tohumidifythe'airinalargespace. Whilethe processed air as it is released may vhave a temperature of 104 E, as in the example given above, it is in the form of latent heat, which is the presentmethod, air circulation may be en- It is unnecessary for the processed air of high vapor pressure to be ejected or circulated into the controlled area, although I prefer to do so, as in the unit shown in Fig. 1, because 01. the

greater speed and efllciency of the equalizing re-" action. All that is necessary is that contact or exposure 'be permitted between the high vapor pressure in the unit and the low vapor pressure in the controlled area.

In the modification shown in Fig. 2, the treated air of' high vapor pressure is circulated within the unit as indicated by the arrows I 00 and is 'not expelled into the room, but contact or exposure of the high pressure vapor with the low pressure vapor of the controlled area is permitted through a grill I02 in the circulatory passage provided in the unit.

I claim:

1. The method of humidifying air in a controlled area, which comprises heating water and a volume of air causing intimate contact between said heated air volume and water whose temperatures are such that the evaporated water absorbed by said air volume has a vapor pressure of more than an inch of mercury, and then bring said high pressure vapor into contact with said controlled area, whereupon vapor flows from the former to the latter independently of any air motion until equal vapor pressure prevails in the contacting air masses, said high pressure vapor having suflicient heat in latent iorm as not to noticeably change the temperature of the controlled area.

2. The method of humidifying air in a controlled area, which comprises heating water and a volume of air separately, spraying the heated water into the heated volume of air whose temperatures are such that the evaporated water absorbed by said air volume has a vapor pressure several times higher than that of said controlled area, impinging the water-sprayed air against a surface to remove moisture in suspension from said air, ,and then bringing said high pressure vapor into. contact with said controlled area whereupon vapor flows i'roni the former to the latter independently of any air motion until equal vapor pressure prevails in the contacting air masses, said high pressure vapor having sumcient heat in latent form as not to noticeably change the tem'peratureoi' the controlled area.

3. The method of humiditying air ina controlled area, which comprises circulating air apart !rom said controlled area, heating water, heating the circulating air at a certain station, causing at another station of said air circulation intimate contact between said heated waterand air whose temperatures are such that the evaporated water absorbed by said heated air has a vapor pressure several times higher than that of said controlled area, and then providing at a third station of said air circulation such communication between said heated air and said controlled area that the former continues in its circulatory path while vapor flows from said heated air to said controlled area independently of any air motion until equal vapor pressure pre- 

